The rotors of dynamoelectric machines conventionally have relatively large diameter cylindrical bodies containing field windings for producing magnetic flux which in turn produces stator current and voltage. These field windings are normally carried in a series of longitudinal slots on the outer circumference and extend the length of the rotor body. Rotation of the body particularly at speeds of 3600 rpm, for example, exert high centrifugal forces on the windings which are retained in the rotor slots through the use of dovetail shaped wedges which extend along the length of the rotor body. The manner in which the windings and rotor slots are shaped, insulated and cooled present formidable design problems, particularly for units designed for long term operation under variable load and environmental conditions. In this regard, since the windings extend axially beyond the rotor body and wedge ends and are subjected to the same rotational forces which tend to thrust the winding end turns in a radially outward direction, specially designed structure must be included to prevent such radial movement, as well as for making electrical connections from an exciter, for example, to the windings.
As to the problem of preventing radial movement of the end turns, it is conventional to enclose the winding end turns with retaining rings attached to the rotor body ends by shrink fitting such rings around a circumferential lip at the end of the rotor body. Other means, such as locking keys and the like, are additionally included to maintain the retaining rings securely on the rotor so as to counteract the effects of thermal expansion on the retaining rings.
As to the manner in which electrical connections may be made to the windings from "bore copper" (insulated conductors embedded in the smaller diameter shafts that extend from both ends of the rotor body, and which are ultimately connected to the exciter/rectifier assembly), such field winding connections as found in the prior art are conventionally brazed copper strip of various configurations. These configurations have exhibited premature failures due to cyclic mechanical and electrical duty requirements, which require the connectors to have particular characteristics.
Thus, the main lead connectors between field windings and bore copper, which extend for the most part in a radial direction, must be sufficiently flexible to accommodate coil movements in both axial and radial directions, which are associated with start up, speed and temperature changes, reversal of rotation direction, as well as the shrink fit characteristics of the retaining rings. Additionally, the main lead connector must be sufficiently rigid to withstand both shock and the centrifugal forces present when the rotor is at operating speed. Still further, the connector as part of its electrical cyclic duty requirements must have sufficient cross section to safely carry electric current up to the maximum design amplitude. The connectors must also allow windings to be depressed to allow the assembly of creepage blocks and insulation in the field slots, the field wedges that hold the winding in the field slots, as well as the retaining ring. Accordingly, a desired connector of sufficient cross section must be somewhat rigid and yet somewhat flexible in order to meet contemplated operating conditions and requirements and avoid premature failure, without requiring brazing (which otherwise makes replacement problematic).
At the same time, electrical connections between the other end of the bore copper and the exciter/rectifier assembly at the other end of the rotor have also not been completely satisfactory. One current practice calls for a litz wire or leaf type connection to be brazed between the bore copper and the exciter/rectifier assembly.
Another current practice is to provide a rigid brazed connection between the bore copper and the exciter/rectifier assembly. In both arrangements, bench assembly of the diode assembly and bore copper is required, followed by assembly to the remainder of the machine in the field. Since these brazed joints are located well within the field bore hole, the main lead terminal must be disassembled and bore copper removed for maintenance and/or replacement of parts, such as the diodes.
We have discovered a connector design for the main lead connector which attains a balance between the above noted factors by exhibiting sufficient rigidity as to be substantially unaffected by the centrifugal forces present at operating speed but which, nevertheless, allows sufficient axial and radial movement of winding end turns due to speed and temperature changes as well as providing sufficient current carrying capacity under such varying conditions.
We have also discovered that this same connector may be utilized-to provide a sliding electrical contact between exciter/rectifier and bore copper which is easy to assembly and disassemble, which also provides for thermal growth, and which allows for replacement of the exciter/rectifier diodes without removal of the bore copper and main lead connectors.
These objects are obtained, in one exemplary embodiment, through the use of a telescoping arrangement whereby a terminal stud (or elongated pin), which is similar to a conventional stud design except for the provision of grooves for accepting the multiple contact bands of a Multilam louvered connector or Belleville spring of the nature disclosed by Neidecker in U.S. Pat. No. 3,453,587 issued Jul. 1, 1969. Such louvered connectors are conventionally used for making resilient electrical contact with adjacent electrical conductors in a manner such as is taught by Hugin in U.S. Pat. No. 4,013,329 issued Mar. 22, 1977.
At the lead end, the terminal stud end (with the louvered connector attached) is inserted in a telescoping manner into a circular cylindrical receptacle element which in turn is brazed or otherwise connected to a field winding. The other end of the terminal stud is attached in a conventional manner to the main lead or bore copper of the rotor shaft. In this manner the individual connector elements may be made of rigid construction. However, a flexible connection allowing for both radial and some axial movement is obtained by way of the resilient louvered connector element which forms good electrical contact between the inner surface of the receptacle element and the outer surface of the terminal stud which is closely received in the receptacle or socket.
At the exciter end, the rectifier assembly is provided with round, copper pins or studs into which dovetail grooves are machined to accept and contain Multilam bands (one or two connectors may be utilized for each pin), in a manner similar to that described above with respect to the main lead connector. The bore copper is provided with mating receptacles or sockets, sized to accept the pins and to provide compression of the band or bands, also as discussed above. A large chamfer on both mating parts provides for ease of assembly, and 0-rings may also be provided on the pins to seal against contamination. For those applications where current end pulses with steep rise times can be expected, it may be necessary to insulate the pins to force all of the current through the Multilam louvers.
The above discussed connector is exemplary only. Other resilient connectors allowing radial and axial movement between the components may be employed as well.
Accordingly, it is an objective of the exemplary embodiment disclosed herein to provide a reliable main lead connector for a dynamoelectric rotor which in additional to providing sufficient current carrying capacity is rigid enough to withstand centrifugal forces developed at operating speeds but which is sufficiently flexible as to accommodate coil movements due to changes in speed and temperature, for example.
It is a further objective of the exemplary embodiment of the invention to provide a reliable connector for the bore copper of a dynamoelectric rotor where the bore copper joins to the exciter/rectifier assembly which provides reliable electric contact, easy assembly and disassembly, and which allows replacement of the rectifier diodes without removal of the bore copper and main lead connectors.
Thus, in its broader aspects, the present invention provides, in one exemplary embodiment, an electrical connector for forming a low resistance current path between the rotor bore copper of a dynamoelectric machine and a related component, the connector comprising a cylindrical receptacle member adapted to be attached to the conductor; an elongated cylindrical member adapted to be connected to the terminal and positioned in telescoping relationship within the receptacle member; at least one resilient electrical connector element located between the cylindrical member and the receptacle member, whereby a low resistance electrical contact between the members is maintained and the members are movable with respect to each other.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.